1. Field of the Invention
The present invention relates generally to systems and methods for circulating a mixture of fluids, solids, and gases around a flow loop for testing purposes. More specifically, the present invention relates to a system and a method for providing the pressure boost necessary to maintain the circulation of a mixture of fluids, solids, and gases around a multiphase flow loop with minimal shearing, cutting, smashing, or other alteration of the solids during the pressure boosting process and the maintenance of an accurate simulation of long, multiphase flow, conduit conditions.
2. Description of the Related Art
The design of long conduit multiphase flow systems depends upon an accurate understanding of the behavior of the various liquid, solid, and gaseous components of the flow over time. Test systems designed to imitate real world long conduit flow have generally failed to provide an environment where such an accurate analysis can be achieved.
Multiphase (gas/liquid/solid) flow test loops generally consist of a conduit loop test section, a separator to remove most of the gas from the liquid and solid components, a gas compressor, a pump for maintaining the flow of the liquid stream with entrained gases and solids, controllers and meters for the liquid stream (with entrained gases and solids), and a mixing section for recombining the pressure boosted components upstream of the loop test section. In some cases, following the test section, the flow stream is heated to melt the solids, the liquid and gas components are then separated, and later recombined downstream of the pressure boosting, flow controllers, meters, and temperature controllers.
When delicate solids are present in a multiphase flow stream, the consequences of pumping the liquid stream (with entrained gases and solids) may be undesirable. In particular, the pressure boosting pump may cut, shear, crush, or otherwise alter the character of the solids. To reduce this problem, pumps with the least solids destructive behavior are selected and the length of the loop is increased, thereby reducing the number of times a particular solid passes through the pump while traversing a given length of test section.
When studying the growth, agglomeration, and other characteristics of solids transport, it is of considerable value to significantly reduce pump degradation. The present invention is directed to providing pressure boosting to circulate multiphase flow components around a test loop without requiring the liquids and solids to pass through a traditional pump. Past efforts along these lines have not been successful.
U.S. Pat. No. 2,451,604, issued to Barnes on Oct. 19, 1948, describes an apparatus for maintaining multiphase flow and for measuring the density of a thixotropic fluid such as the drilling mud used in the rotary drilling of wells. In the Barnes invention, mud is diverted from the flow stream and is passed through a chamber that establishes a vertical hydrostatic head whose pressure differentials are measured through a standard mercury-based pressure sensor.
U.S. Pat. No. 2,952,152, issued to Fisher et al. on Sep. 13, 1960, describes a gel point indicator directed to identifying the temperature at which a fluid gels. The apparatus describes a vertical column (similar in some respects to a vertical hydrostatic head structure) that provides the necessary cooling for the system but otherwise involves no continuous flow of a fluid.
U.S. Pat. No. 3,690,184, issued to Chadenson on Sep. 12, 1972, describes an apparatus for statistically measuring the average density of a liquid circulating in a pipeline. Fluid is diverted into a column and the density is measured by comparing the hydrostatic pressure between the column and a reference column.
U.S. Pat. No. 4,274,283, issued to Maus et al. on Jun. 23, 1981, describes an apparatus and method for measuring fluid gel strength such as that for drilling mud. In this system, the flow of drilling mud through a conduit is interrupted and a differential pressure between various points in the flow is measured.
U.S. Pat. No. 4,660,414, issued to Hatton et al. on Apr. 28, 1987, describes a petroleum stream monitoring system and method wherein a crude oil production stream flows through a separating device to remove substantially all gas components. Various parameters are measured in this system including temperature, gas velocity, liquid flow, etc., thereby providing indications of gas, oil, and water flow rates through the multiphase system.
U.S. Pat. No. 4,760,742, issued to Hatton on Aug. 2, 1988, describes a multiphase petroleum stream monitoring system and method similar to the '414 Hatton patent and also discloses a gas separation means.
U.S. Pat. No. 5,251,488, issued to Haberman et al. on Oct. 12, 1993, discloses a multiphase volume and flow test instrument wherein fluid is diverted into a test section and either allowed to separate into its various phase components or chemically aided in this process. Floats within the apparatus, tuned to the densities of the various components, are used to determine the relative quantities of those components within the flow.
U.S. Pat. No. 5,394,339, issued to Jones on Feb. 28, 1995, describes an apparatus for analyzing oil well production fluid wherein the fluid is diverted to a test pipe where various phase components are measured.
Most of the previous attempts to analyze, measure, and regulate the flow of fluids in a system for the purposes of testing and evaluation, have focused on specific efforts to identify the relative composition of the flow compounds and/or to separate the various components at points in the flow for specific analysis and study. Efforts to accurately simulate the environment within which fluids must perform in actual field conditions have been limited and inadequate in most situations. In almost every instance, the effort to accurately simulate a long conduit flow for fluids has failed to recreate accurately the flow environment for such fluids. This failure relates to the inability to appropriately control and sustain the multiphase composition of the fluid at the same time as the flow itself is being maintained constant. Well known methods for maintaining flow generally work against the maintenance of a consistent and constant liquid/gas/solid composition.
It would be desirable, therefore, to have a system that imitates the environment within which fluids are likely to flow in real case scenarios and yet provide such a system with a closed loop structure on a limited dimensional scale that will make the testing and analysis practical. Such a system would have to be able to separate the components, boost the pressure in each of the components to maintain flow, and recombine the components in such a way that the composition of the flow after pressure boosting is as close as possible to the composition prior to such actions.